Challenge

Project-1: Powertrain for aircraft in runways

SSunil Rathod12 Nov 2021

Project-1: Powertrain for aircraft in runways

OBJECTIVE:

1. Search and list out the total weight of various types of aircrafts.

2. Is there any difference between ground speed and air speed?

3. Why is it not recommended to use aircraft engine power to move it on the ground at Airport?

4. How an aircraft is pushed to runway when its ready to take off?

5. Learn about take off power, tyre design, rolling resistance, tyre pressure, brake forces when landing.

6. A. With necessary assumptions, calculate the force and power required to push / pull an aircraft by a towing vehicle.

B. Develop the model for the calculated force and power using Simulink.

7. A. Design an electric powertrain with type of motor, it’s power rating, and energy requirement to fulfill aircraft towing application in Simulink. Estimate the duty cycle range to control the aircraft speed from zero to highest. Make all required assumptions. Prepare a table of assumed parameters. Draw a block diagram of powertrain.

STUDY1:

1. Search and list out the total weight of various types of aircrafts.

1. Aircraft Gross Weight:

The aircraft gross weight (also known as the all-up weight and abbreviated AUW) is the total aircraft weight at any moment during the flight or ground operation.

An aircraft's gross weight will decrease during a flight due to fuel and oil consumption. An aircraft's gross weight may also vary during a flight due to payload dropping.

At the moment of releasing its brakes, the gross weight of an aircraft is equal to its takeoff weight. During flight, an aircraft's gross weight is referred to as the en-route weight or in-flight weight.

Weight of Various Types of Aircraft Weight:

1.Glider

Glider is a fixed wing plane that is supported in flight by the dynamic reaction of the air against its lifting surfaces, and whose free weight does not depend on an engine. Most gliders do not have an engine, although motor glider have small engines for extending their flight when necessary by sustaining the altitude (normally a sailplane is on a continuously descending slope) with some being powerful enough to take off self launch.

Weight of Glider planes:110kg-200kg

2. Powered Lift

A powered lift aircraft takes off vertically under engine power but uses a fixed wing for horizontal flight. These aircraft do not need a long runway to take off and land, like helicopters, but they have a speed and performance similar to standard fixed wing aircraft in combat or other situations.

Weight: 160 kgs

3.Fighter Aircraft

A fighter aircraft, often referred to simply as a fighter, is a military fixed wing aircraft designed primarily for air to air combat against other aircraft. The key performance features of a fighter include not only its firepower but also its high speed and manuverability relative to the target aircraft.

Weight:13500 kgs

4.Transport Planes:

Military transport aircraft or military cargo aircraft are used to airlift troops, weapons and other military equipment to support military operations. Transport aircraft can be used for both strategic and tactical missions, and are often diverted to civil emergency relief missions.

Weight: 250,000 kgs

5. Aerobatic Planes

An aerobatic aircraft is an aerodyne (a heavier-than-air aircraft) used in aerobatics, both for flight exhibitions and aerobatic competitions

Weight:771 kgs

2. Difference between ground speed and air speed

Ground Speed

Ground speed is the airplane's speed relative to the surface of the Earth

Ground speed is what determines how fast an aircraft will get to its destination

Ground speed is simply the sum of airspeed and wind speed.

Air speed

Airspeed is the speed relative to the air it is flying in.

Airspeed is what determines whether there is enough airflow around an aircraft to make it fly

It is independent of ground speed.

3.Why is it not recommended to use aircraft engine power to move it on the ground at Airport?

Towing is coupling two or more objects together so that they may be pulled by a designated power source or sources. The towing source may be a motorized land vehicle, vessel, animal, or human, and the load being anything that can be pulled

Although many aircraft are thrust (a procedure referred to as a powerback), the resulting jet prop might cause damage to the terminal building or equipment. Engines close to the ground may also blow sand and debris forward and then suck them into the engine, causing damage to the engine. A pushback is therefore the preferred method to move the aircraft away from the gate.

Although most aircraft are capable of moving themselves backwards on the ground using reverse thrust, a procedure called as a powerback, it is not typically done due to the following reasons:

• The jet blast from the engines can damage the terminal building and nearby equipment. It can even throw away people standing nearby.

• Engines can blow sand and debris. Engines can suck in sand and debris which can cause serious damage to the engine.

• It is easier for the truck driver to see the surroundings better than the pilot sitting in the cockpit with limited windows.

• The pushback truck driver knows the airport better than the pilot. The plane engines are very loud. This noise can add up substantially when multiple planes are moving around the airport. It won't be a pleasant experience for people sitting inside the terminal. as most people don't even like the sound of powerful motor-bikes.

• It saves fuel. Virgin Atlantic had proposed a new system in which the pushback trucks will push the plane all the way to the runway to save fuel and reduce impact on nearby environment.

4. aircraft is pushed to runway when its ready to take off.

Taxiing is the movement of an aircraft on the ground, under its own power, in contrast to towing or push-back where the aircraft is moved by a tug. The aircraft usually moves on wheels, but the term also includes aircraft with skis or floats (for water-based travel).

The power for taxiing comes from the engines itself. If it is a propeller powered aircraft, the propeller provides thrust and pulls the aircraft, like it would in air. If it is a jet engine, the exhaust air that comes out of the engine creates a forward force due to Newton's third law and moves the airplane.

Airliners have nose wheel steering, controlled by a cockpit control called a tiller. The tiller allows nose wheel to rotate at quite extreme angles making tighter turns possible. It also reduces the fuel consumption as you do not need much engine power during taxiing, If rudders were used, the power has to be increased to make sure sufficient air flows over the rudder surface to make it effective.

Once on the take off roll and the airplane gains sufficient speed i.e. enough air flows over the rudders, pilots go back to using the rudder pedals to maintain the centre line.

Some large airplanes with multi wheel main gears have a tendency to scrub the tyres on the tarmac when nose wheel is steered. To counter this problem, an automatic main gear steering is inbuilt in the aircraft. This makes the main gears turn the opposite direction to that of the nose wheel, greatly decreasing the wear on the tyres.

Small general aviation aircraft uses the rudder for turns during taxi. They don't have a separate control for nose wheel. In such airplanes, to make tighter turns, you could use differential braking. That is, if you want to make a tight turn for example to the left, you would push the upper part of your left rudder pedal which would apply left braking. This allows the airplane to make a sharper turn to the left.

5. Take off power, tyre design, rolling resistance, tyre pressure, brake forces when landing.

a. Take off Performance:

Take off performance can be predicted using a simple measure of the acceleration of the aircraft along the runway based on force equilibrium.

The forces involved will be,

T - Thrust of propulsion system pushing aircraft along runway.

D - Aerodynamic Drag of vehicle resisting the aircraft motion

F - Rolling resistance friction due to the contact of wheels or skids on the ground.

During take-off run the imbalance in these forces will produce an acceleration along the runway

`(dv)/dt=T-D-F`/m

The procedure for take-off will be that the vehicle will accelerate until it reaches a safe initial flying speed. The pilot can then rotate the vehicle to an attitude to produce climb lift and it will ascend from the ground. The determination of this safe flying speed or rotation speed, VR. is a critical factor in determining take-off performance

For safety reasons Va is usually determined as being 1.1 * VSTALL

VSTALL : Is the lowest speed that the aircraft can be flown before the airflow starts to separate from wings as the angle of attack becomes too great. The wing is assumed in this case to be in take-off configuration or "clean".

It can be calculated based on knowledge of the aircraft take-off configuration and hence the maximum achievable lift coefficient `C_L(max)`

As shown in the previous section to maintain level flight the lift produced must equal the weight, hence the stall speed can be calculated as,

`V_(stall)=sqrt(W/(1/2)C_(L(MAX)rhoS`

b.Tyre Design of aircrafts:

When it comes to safety, tyres are one of the most important components of aircraft. They help to absorb the shock of landing and provide cushioning.

It also provides the necessary traction for braking and stopping of an aircraft. An aircraft tyre is designed to withstand extremely heavy loads while landing, take off, taxing and parking.

The number of wheels required for aircraft increases with the weight of the aircraft, as the weight of the aeroplane needs to be distributed more evenly.

Carcass plies are used to form the tire. They are sometimes called casing plies. An aircraft tyre is constructed for the purpose it serves. Unlike an automobile or truck tyre, it does not have to carry a load for a long period of continuous operation However, an aircraft tyre absorbs the high impact loads of landing and also it's operating at high speeds for a short time when required.

Retreading - Rtreading is methods of restoring a worn tyre by renewing the tread area or by renewing the tread area plus one or both sidewalls. Repairs are included in the tyre retreading process.

Load Rating - Load rating is the maximum permissible load at a specified inflation pressure.

Ply Rating - Ply Rating is used to identify the maximum recommended load rating and inflation pressure for a specified tyre. It is an index of tyre strength. Speed Rating-The speed rating is the maximum takeoff speed to which the tyre has been tested.

Skid Depth - Skid depth is the distance between the tread surface and the deepest groove as measured in the mould. Aircraft tyres must have an approved speed and load rating and have sufficient clearance when retracted through landing gear to allow for tyre growth. Tyre growth is the increase in the size of the tyre due to centrifugal forces at high speed.

c.Rolling Resistance:

Rolling resistance, sometimes called rolling friction or rolling drag, is the force resisting the motion when a body (such as a ball, tire, or wheel) rolls on a surface. It is mainly caused by effects; thnon elastic at is, not all the energy needed for deformation (or movement) of the wheel, roadbed, etc., is recovered when the pressure is removed. Two forms of this are hysterisis losses, and permanent plastic deformation of the object or the surface (e.g. soil). Another cause of rolling resistance lies in the slippage between the wheel and the surface, which dissipates energy. Note that only the last of these effects involves friction, therefore the name "rolling friction" is to an extent a misnomer.

The rolling resistance can be expressed as

`F_r=cW.............................(1)`

where `F_r`= rolling resistance or rolling friction (N, `Ib_f`)

C = rolling resistance coefficient - dimensionless (coefficient of rolling friction-CRF)

`W=m a_g`

`W=`normal force - or weight - of the body (N, `Ib_f`)

m = mass of body (kg, Ib)

`a_g`= acceleration of gravity (`9.81 m/s^2,32.174 ft/s^2)

d.Tyre Pressure :

Car tyres aren't just unsafe when they're old and worn out - you need to ensure you know what tyre pressure you have in your tyres when you drive it because there are critical safety and economic implications. Car tyre pressure is a measurement of how much air is in your pneumatic tyre and ensures the tyres wear evenly and maintain the correct level of grip on the road surface. This is commonly expressed as PSI.or pounds-per-square-inch.

e. Brake forces:

Braking an aircraft is a challenging job for most of the pilots especially during landing in a rainy and cross wind environment.

Inorder to encounter this kinds of problem pilots usually make use of spoilers and reverse thust method inorder to have a safe landing so that the energy required to apply brakes on tires can be reduced and henceforth they do not skid.

Now there is method which determines the brake force for aircrafts and they are as follows:

`K=1/2mv^2`

where m = mass of aircraft and v = velocity of aircraft.

A typical commercial landing speed will range between 150 to 165 MPH. And for passenger flight it is about 166 to 172mph.

6. A. With necessary assumptions, calculate the force and power required to push / pull an aircraft by a towing vehicle.

To push or pull an aircraft by a towing vehicle is have three types of forces will act on that vehicle.

Those are

• Rolling Resistance Force

• Aerodynamic Drag Force

• Hill Climbing Force.

Push/Pull Power Calculation of Towing Vehicle.

Let's assume,

Towing Vehicle mass = 50000 kg

Aircraft mass = 183700 kg

Total mass of the vehicle = (50000+183700)=233700 kg

Speed of the vehicle (V) = 10 km/hr = 2.77 m/s\

Rolling Resistance Force

`F_(rr)=urr*m*g`

= 0.013*233700*9.8

= 29773.38N

Aerodynamic Drag Force

`F_(ad)=(1/2)*rho*v^2*A*(Cd_t+Cda)`

=`(1/2)*1.225*(2.778)^2*20*(0.5+0.045)`

= 51.514

Hill Climbing Force

`F_(hc)=m*g*sinphi`

`=233700*9.8*sin0`

`=0N`

Total Traction Force

`F_(te) = F_(rr)+F_(ad)+F_(hc)`

= 29773.38+51.514+0

= 29824.894N

Total Power

=`(F_(te)*V)/1000`

= 82.84KW

B. Develop the model for the calculated force and power using Simulink

• Rolling Resistance Force

• Aerodynamic Drag Force

• Hill Climbing Force

MODEL:

7A. Design an electric powertrain with type of motor, it’s power rating, and energy requirement to fulfill aircraft towing application in Simulink. Estimate the duty cycle range to control the aircraft speed from zero to highest. Make all required assumptions. Prepare a table of assumed parameters. Draw a block diagram of powertrain.

SIMULINK MODEL OF POWERTRAIN OF AN AIR-CRAFT TOWING VEHICLE

Estimation of Duty cycle: As we know that the power required for towing vehicle to push/pull is equall to 45.60kW. For this model we have considered the motor REB 90 for drive train.

Considering 60kW as continous power, so the voltage will be 400V. Battery power is considered to be 550V. we know that duty cycle is given by d=Vo/Vb.

d=3400/550, => 0.7272.

There will also be losses due to the resistance of FET and inductance. Correction factor is considered to be 90% ,that makes us consider that there is 10% loss, So the voltage which is demanded by the motor should be 10% more than the required voltage.d =0.7272*(1+0.1)= 0.799-0.8. so here the voltage demand is 440V from the battery.

Mass of the aircraft 580000kg

Mass of towing vehicle 1000kg

Coefficient of rolling resistance 0.002

Drag coefficient 0.025

Air-density 1.125kg/m^3

Frontal area 150m^2

Velocity 4m/s

Uphill gradient 0 deg

Battery voltage 550V

Correction factor 0.8

INPUT: